This invention relates generally to methods and apparatus for ultrasound hyperthermia, and, more particularly, relates to apparatus and methods for measuring tissue temperature and other tissue properties in hyperthermic treatment of internal cancers and other diseases which respond to temperature elevation.
Production of a controllable level of temperature elevation or hyperthermia at pre-selected locations and volumes of tissue has been found to be of significant therapeutic value in the treatment of Patients with cancer or other diseases.
Well-managed clinical application of hyperthermia requires the ability to produce specific, well-characterized temperature elevations in precisely selected volumes of tissue that comprise the malignancy. The corresponding engineering requirement is the ability to control the temporal and spatial characteristics of the absorbed thermal dose so as to produce the desired temperature distribution for the specific malignancy being treated.
The achievement and accurate measurement of the elevated temperature distribution is thus of primary importance in any hyperthermia system. An ideal hyperthermia system would provide control of the temporal and spatial characteristics of the heat source, whether ultrasound, microwave or radio-frequency, in order to shape the volumetric power deposition pattern to the specific requirements of the malignancy.
In view of the significant tissue temperature gradients that can exist during hyperthermia as a consequence of differences in blood flow and thermal conductivity of tissue--both of which are markedly altered with temperature--and the evidence that temperature control is crucial to successful hyperthermia treatment, it is equally crucial that accurate high-resolution thermometry at multiple sites in the treatment volume be available. Temperature gradients will be greatest at the boundaries of differential energy absorption, perfusion and conductivity, and thus, the temperature at the tumor margin or proliferating edge, as well as other locations within the tumor, must be known.
The state of tissue perfusion is a primary component in local heat transport, the regulation of which is crucial to hyperthermia. Thus, planning and optimization of hyperthermia therapy requires knowledge of the distribution and magnitude of the local level of perfusion. Because blood flow has a significant influence on the temperature distribution in tissue during hyperthermia, knowledge of the magnitude and the distribution of perfusion in both the tumor and surrounding host tissue is necessary for accurate thermal therapy planning or predictive modeling of temperature distribution during hyperthermia. Additionally, information on local blood flow in the treatment volume during hyperthermia is essential to enable effective sequencing of hyperthermic and radiation therapy or chemotherapy.
It would therefore be useful to monitor temperature distributions accurately during hyperthermic treatments of cancer while minimally perturbing the local environment. It would also be desirable to provide a means for obtaining temperature measurements at a plurality of tissue locations, together with other measurements of tissue characteristics including blood perfusion, thermal conductivity and thermal diffusivity.
Furthermore, in ultrasound hyperthermia systems, it would be desirable to obtain acoustic attenuation, acoustic absorption and sound Propagation velocity data, together with information representative of the separation between the ultrasound source and the target area.
Conventional methods for temperature measurements in vivo involve the insertion of catheters or probes which contain one or more thermistors or thermocouple junctions. Such a technique is minimally invasive and, if correctly implemented, provides accurate temperature measurements in real-time.
Conventional hyperthermia probes, however, cannot provide measurements of properties other than temperature. Such apparatus, for example, cannot supply data representative of thermal diffusion, tissue perfusion, acoustic absorption, acoustic attenuation, onset of cavitation, and sound propagation velocity, essential to planning effective and safe treatment. Moreover, conventional probes for hyperthermia treatment cannot provide other useful data such as insonation head-to-probe distance, or the separation between multiple probes. In addition, conventional probes are non-flexible, and present a risk of tissue tearing due to patient movement or movement of internal organs.
Accordingly, there exists a need for hyperthermia probe apparatus and methods which can measure a variety of physical properties of the tissue, and which can be used to provide positional information to the hyperthermia system computer and the operator.
It is accordingly an object of the invention to provide improved hyperthermia probe methods and apparatus.
It is another object of the invention to provide methods and apparatus for measuring temperature, thermal diffusion, tissue perfusion, local intensity, energy absorption, onset of cavitation, and other properties in hyperthermia treatment.
It is a further object of the invention to provide a probe which can provide positional data representative of relative source, probe and tissue separations.
Other general and specific objects of the invention will in part be obvious and will in part appear hereinafter.